Long-Term Impact of Neonatal Intake of Oleanolic Acid on the Expression of AMP-Activated Protein Kinase, Adiponectin and Inflammatory Cytokines in Rats Fed with a High Fructose Diet

Abstract

AMP-activated protein kinase (AMPK) is known to regulate both glucose and lipid metabolism, which play vital roles in the development of metabolic syndrome. One way of regulating AMPK is through hormonal activation using adiponectin. Patients diagnosed with type-2 diabetes (T2D) and obesity exhibit low adiponectin concentration levels in their blood. Moreover, studies have also shown that inflammatory processes play a significant role in the etiology of these metabolic diseases. In this study, the long-term effects of neonatal intake of oleanolic acid (OA) on the AMPK gene, genes associated with glucose transport and lipid metabolism, adiponectin levels, and inflammatory biomarkers in rats fed with a high fructose diet were investigated. Seven day old pups were randomly divided into five groups and treated as follows; 0.5% dimethylsulphoxide v/v in distilled water vehicle control (CON), oleanolic acid (OA, 60 mg/kg), high fructose diet (HF, 20% w/v), high fructose diet combined with oleanolic acid (HF+OA), and high fructose diet combined with metformin (HF+MET, 500 mg/kg). The treatments were administered once daily until day 14. The rats were then weaned at day 21 and fed standard rat chow and had ad libitum access to plain drinking water until day 112. The quantitative polymerase chain reaction (qPCR) was used to analyze the gene expressions of AMPK, Glut-4, Cpt-1, AdipoR1, AdipoR2, TNF-α, and IL-6 in the skeletal muscles. Bio-Plex Pro magnetic bead-based assay was used to measure plasma levels of inflammatory markers (TNF-α, IL-6, VEGF, and MCP-1) while ELISA kits were used to measure adiponectin concentration in blood plasma. The results obtained in this study showed that neonatal supplementation with OA significantly increased AMPK gene expression approximately ~4-fold in OA fed rats compared to those that were fed with HF alone. In addition, glut-4 gene expression was also significantly higher in the OA treatment group compared to all the other experimental groups except the CON group whereas Cpt-1 gene was more expressed when OA was administered alone. Together, these results indicated that OA can play a role in glucose and lipid metabolism gene regulation. Furthermore, the results showed that the OA group had ~1.5-fold increase in adiponectin concentration when comparedto the HF group. Moreover, HF increased levels of inflammatory cytokines, which was attenuated by neonatal administration of OA. Plasma concentration and gene expression in the skeletal muscle for TNF-α and IL-6 were significantly increased in rats that were treated with HF alone when compared to all the other groups. On the contrary, the high levels of TNF-α and IL-6 were reduced when OA was administered. These findings suggest that intake of oleanolic acid during the neonatal stage of development could be a potential strategic intervention for the long-term prevention of metabolic diseases such as T2D and obesity.

Potential Protective Effect of Oleanolic Acid on the Components of Metabolic Syndrome: A Systematic Review

“…In agreement with these results, a significant reduction in the gene expression of IL-1β and IL-6 in liver and adipose tissue, as well as of TNFα in adipose tissue of mice was observed by Djeziri et al [40]. In addition, Matumba et al [45] administered OA to neonatal rats fed with a high fructose (HF) diet, and they observed a decrease of IL-6 and TNFα plasma levels and a reduction of their gene expression at the end of the experiment. An increase of plasma level of adiponectin was also observed by these authors [45].…”

“…In addition, Matumba et al [45] administered OA to neonatal rats fed with a high fructose (HF) diet, and they observed a decrease of IL-6 and TNFα plasma levels and a reduction of their gene expression at the end of the experiment. An increase of plasma level of adiponectin was also observed by these authors [45]. In summary, OA was able to decrease both the serum levels and gene expression of the proinflammatory cytokines IL-1β, IL-6, and TNFα.…”

“…Dysregulation of adipokines plays a main role in the association between insulin resistance and oxidative stress [55]. Matumba et al [45] showed that OA enhanced adiponectin plasma concentrations, which could result on greater insulin sensitivity [56] due to its insulin-sensitizing properties through enhancing hepatic IRS-2 expression [57]. In the present review, we found that OA increased serum leptin levels in hyperlipidemic patients [49], an adipokine that favors the synthesis of proinflammatory cytokines [54].…”

“…It is noteworthy that the decrease in both serum levels [30,34,35,44,45] and gene expressions [40,45] of proinflammatory cytokines reported in our review, probably due to the modulatory effect of OA on NF-kB [17], could result in an improvement of insulin secretion and beta-cell function because proinflammatory cytokines, whose levels are higher in obese individuals, have an important role in the development of insulin resistance [8,9,10]. Moreover, [17,30,34,35,40,44,45].…”

Oleanolic Acid Exerts a Neuroprotective Effect Against Microglial Cell Activation by Modulating Cytokine Release and Antioxidant Defense Systems

“…The data shown in this study are consistent with other previously reported for OA and related triterpenoids. Matumba et al [54] described a similar response to OA in rats fed a high-fructose diet, showing that the effect of OA on the repression of TNF-α levels in skeletal muscle cells was more modest than that on gene expression. Fan et al [55] investigated the potential of hyperoside, a galactoside of quercetin, to inhibit inflammatory mediators in BV2 microglial cells stimulated with LPS.…”